How many years will a new rooflight give me?

A rooflight is not a single object with a single expiry date. It is a frame, a sealed glass unit fitted inside that frame, and a run of seals and flashings that keep water out of the join between the two. Each ages at its own pace, and the one that gives up first is rarely the one people expect.

An aluminium or well-made composite frame can go on doing its job for decades. The glass unit inside it is a different story: two or three panes of glass, an air or gas gap between them, and a spacer bar sealed at the edge to keep that gap dry. That seal is the part with the shortest clock, and once it starts to let go, the view is what suffers first, long before the frame shows any sign of age.

The frame carries the glass, the hardware and, on a flat roof, the upstand that lifts the unit clear of standing water. Material decides most of its life.

• Aluminium and powder-coated composite: the longest-lived part of any rooflight. A properly finished aluminium frame does not rot, and the coating protects it from UV and weather for a working life measured in decades rather than years.
• Timber, treated and factory-finished: can match aluminium for life if the finish is kept sound and water is not left sitting against joints, but it needs that upkeep in a way metal frames do not.
• uPVC frames: can discolour and stiffen with UV exposure over time, which changes how well opening lights close and seal, even where the glass unit inside is still perfectly sound.

On a Fletton-brick terrace with a shallow pitch, or a flat-roofed extension in one of the new-town townships such as Bretton, Orton or Werrington, the frame and its upstand are doing extra work against standing water and thermal movement compared with a steep slate roof. Around Stamford, where Collyweston stone slate calls for a slim conservation profile, the same principle holds: it is the finish and the detailing at the edges, not the glass, that decide how long the frame stays sound.

The sealed unit is the part that actually gives you the view, and it is also the part with the shortest working life of the three. Between the panes sits a gap, often filled with argon, held in by a spacer bar and an edge seal.

That edge seal is doing a harder job than it looks. It is holding back weather, UV and years of thermal movement as the glass heats and cools with every sunny afternoon and cold night. Once it starts to let go, whatever is in the gap slowly escapes and moist air finds its way in instead. The tell is condensation between the panes rather than on either surface, a haze that no amount of cleaning will shift because it is sealed on the wrong side of the glass. Our page on why a skylight can look dirty from inside walks through how to tell that apart from ordinary dust or surface condensation.

A rooflight facing a low winter sun, or one on a shallow pitch that never quite dries between showers, works its seal harder than one set higher and steeper. That is one reason orientation and pitch are decided at the planning stage rather than left to chance, alongside the glass specification covered on what glass suits a skylight.

A few factors move all three clocks, but not by the same amount, and not in the same direction.

Coatings extend the glass unit's practical life without touching the seal at all. A self-cleaning outer coating on a low pitch reduces the grime that would otherwise sit on the glass and shorten how long the view stays sharp, and a solar control coating cuts the heat cycling that stresses the seal on a south-facing slope. Both are covered in more depth on keeping rooflight glass clear for years.

Installation matters as much as the product. A unit bedded and weathered correctly on day one, with the right falls and flashings around it, is not fighting water ingress from the start. That is a large part of what a proper survey and fit are for, and what we cover on what happens on rooflight installation day.

Because Clearview plans every rooflight around the sightline from the bed, the sofa or the sink, a failing seal matters to us for a reason beyond warmth: it is the one fault that spoils the view without anything visibly breaking. The frame still looks straight, the glass is not cracked, but the sky through it turns milky at the edges and then across the whole pane.

That is different from tint, which is a deliberate coating choice rather than a fault; our page on whether tinted rooflight glass spoils the view explains that distinction. A misting seal is not a look anyone chose. It is worth knowing the difference before deciding whether a unit needs attention or simply needs a wipe.

A failed seal cannot be renewed from outside. Once the gap between the panes is compromised, the sealed unit as a whole has reached the end of its working life, even where the frame around it is still sound. Our guide to signs your skylights are due for replacement sets out the visible clues, and is it worth replacing old skylights weighs the decision without any scare stories attached to it.

A sound frame is good reason to replace only the glazing where that is possible, rather than the whole unit. Where the frame itself has reached the end of its own clock, our guide to replacing old rooflights covers what a full replacement involves, including the chance to fit a slimmer frame and a better sightline than the original gave.

Every quote we write, whether for a first rooflight or a replacement, comes with a sightline sketch showing the view you will actually get, described on the sightline sketch page, and every installation is carried out to current Building Regulations with a 10-year workmanship guarantee. See the full range on skylight and rooflight installation in Peterborough, or book a home visit to have the frame, seal and glass in your own roof looked at properly.

Does a longer guarantee mean the glass will last longer?

A workmanship guarantee covers the fitting, not how long the sealed unit itself keeps its seal. The two are related, since a badly bedded unit fails sooner, but the guarantee is a promise about the installation rather than a stated lifespan for the glass.

Can just the sealed unit be replaced, leaving the frame in place?

Often, yes, where the frame is sound and the glazing system allows the unit to be lifted out and a new one bedded in. It depends on the product and how it was originally fitted, which is worth checking before assuming a full replacement is needed.

Do triple-glazed units last longer than double-glazed ones?

Not automatically. An extra pane means an extra edge seal doing the same job, so the number of panes affects warmth and noise more than it affects how long the seal itself holds.

Is a misted rooflight a sign the frame is failing too?

Not usually. Misting between the panes is a seal problem specific to the glass unit, and a frame can carry on for years afterwards. It is still worth having both checked together, since whatever caused water to sit against the seal may be worth correcting before a new unit goes in.